In many applications in the fluids field, in particular for cooling vehicle heat engines, thermostatic valves are used to distribute a fluid entering various circulation channels, based on the temperature of that fluid. These valves are said to be thermostatic because the movement of their inner closure member(s) is controlled by a thermostatic element, i.e., an element that comprises a cup containing a thermally expanding material and a piston able to slide relative to the cup under the action of the thermally expanding material when the latter expands.
To distribute the fluid as a function of other parameters, in particular conditions outside the valve, such as the ambient temperature or the load of the vehicle propelled by the engine equipped with the valve, it is known to incorporate electric heating of the thermally expandable material into the valve, which makes it possible to control the valve from outside it, independently of or in addition to the temperature of the incoming fluid, in particular using an onboard computer in the vehicle programmed appropriately. In practice, a heating resistance is arranged inside the aforementioned piston or a similar tube: for example, by immobilizing the piston in the moving case of the valve, the power supply of the resistance causes the temperature of the thermally expanding material to increase, which, by extension of the latter, causes the cup to slide around the piston, a closure member being supported by that cup to act on the flow of fluid through the valve.
To provide electricity to the heating resistance, one possibility, known from DE-A-103 03 133, consists of the electrically conductive wires, which extend from the resistance to the outside of the aforementioned tube while passing through a terminal part of the latter, and the free ends of which are electrically connected to connecting steps to be connected to an external current source, being directly coated with the plastic material of the housing during molding of the latter around the aforementioned terminal part of the tube. However, this solution is delicate to manufacture, since during molding of the case, the plastic material injected so as to overmold the terminal part of the tube tends to pull, or even pull out, the electrical wires, unless sophisticated and therefore expensive injection molds are used, which furthermore need to be modified when the arrangement of the wires is changed, typically depending on the position, on the case, of the aforementioned connecting pads.
EP-A-0,853,267 proposes overmolding both the terminal part of a heating tube, similar to what is mentioned above, and the electrical wires that leave that tube, with a plastic coating material, so as to form a module, which is next attached in a single piece to the rest of the thermostatic valve, by screwing a thread formed by that plastic material in a complementary tapping, formed by the housing of the valve. The implementation of this solution has the same drawbacks as above, during the injection of the aforementioned plastic coating material.
WO-A-2011/010051 mentions a possible pre-injection of plastic around electrical wires similar to those mentioned thus far, but only at the end of those wires, at which they are electrically connected to connecting studs. This pre-injection is followed by an injection of plastic to form the housing of the valve, then coating all of the rest of the wires, extending outside the tube, as well as the terminal part of the tube.